The present invention relates to pretreatment chemicals for metal materials to be painted. The metal materials include a steel plated with a metal (referred to as a metal-plated steel hereinafter), a non-plated steel or a metal other than steel. The present invention particularly relates to non-chromium pretreatment chemicals for metal materials to be painted, a metal-plated steel or a non-plated steel used as building materials or electrical household appliances in which a severe processing such as press or bending is needed after being painted, a method for pretreatment and a metal material treated thereby.
As the pretreatment chemicals used in the pretreatment for painting mentioned above, a reaction type or a coating type chromate-containing treating agent have been usually used. For example, a treating method where after the chromate treating agents are coated, an aqueous solution of an organic polymer resin is applied is disclosed in Japanese Patent Application KOKAI No.202084/1987. But considering the nowadays tendency of environmental regulation, there is the possibility such chromate-containing anticorrosive agent is restricted in use because of the high toxicity and the carcinogenicity. In this situation, Japanese Publication No.31593/1984 discloses a method of treating a metal surface without chromium. This method basically relates to a formation of phosphoric acid conversion film, which is insufficient for achieving a high adhesion of the painted film in the use of tough bending processing. An anticorrosive agent disclosed in Japanese Patent Application No.195244/1993 is not a perfect pollution-free treating agent, as it contains fluorine ion and heavy metal, and it is far from an ideal non-chromium treating agent in view of the high load in waste water treatment.